Cyst nematodes attacking Arkansas beans

“I imagine it will drive yields down,” says Cheney. “How much, I don’t know, but it looks like tough going from here on in those fields. I can see yield reduction from 10 percent to 40 percent, easy.

“We haven’t confirmed the race yet, but we’re pretty sure it’s either Race 5 or Race 6. On one field, the farmer has had Race 5 before. He planted several varieties – one with no resistance and one resistant to 3 and 14. We feel it’s probably a new race that there’s no resistance to. If it’s 2, 5, 6 or 9 there’s trouble brewing.”

Now that it’s getting drier and warmer, nematodes are starting to show up in fields around the state.

During the last week of June, Brent Griffin, an Extension agent based in Des Arc, was called out to a soybean field because the crop wasn’t growing well.

“You can see the old rice levees in the field and at first they thought it might have been due to salt injury,” says Cheney. “And there is a little salt out there. But Brent shoveled a plant out of the ground and the roots were covered with cyst nematodes. You could see the nematodes easily. In 2001, this farmer had a problem with nematodes, so he figured that was the culprit and called other folks in.”

One good way to sample plants for nematodes is to pull them, wash the roots off and then let them air dry. It’s usually easy to see nematodes when the roots are dry.

“What was shocking about the Prairie County fields is you could just lean over, pull a plant and immediately see cysts all over the roots,” says Chris Tingle, Arkansas Extension soybean specialist.

“Nematodes were clustered all over the roots in remarkably high numbers,” he noted. “Nematodes didn’t leave fields over the last year. They’ve been sitting in the soil waiting for their chance. Being a pest below the ground, we have to wait for symptoms above the ground before picking up on the problem. Well, we’re picking up plenty now.”

Cheney says the Des Arc farmer plans to keep the fields and irrigate them as much as possible. But Cliff Coker, Extension plant pathologist, points out that the root systems are already injured and are now susceptible to SDS, charcoal rot and anything else that attacks a plant’s roots.

“Just from eyeballing affected fields, I’d say the situation is pretty serious,” says Coker. “It’s not exceptionally bad yet. Right now, things aren’t as serious as they were in 2001. But it’s a lot more severe than last year. Growers are going to have their yields hit, no doubt.

“While this has shown up in the Grand Prairie, I think it’s probably elsewhere. I’m fearful that a lot of growers aren’t looking for nematodes. Since yields weren’t hurt badly from nematodes last year, I think a lot of folks aren’t paying attention yet. But, considering where we’ve found them and the severity, I think this is an indication that nematode damage will be pretty serious this season.”

Tingle agrees and says many people in agriculture “are sitting on pins and needles waiting to see how bad this nematode situation is going to be. Potentially, it could be very bad. Looking back at 2001, nematodes tore us up. We could easily see a similar dose this season. In traveling the state and looking out across fields there are a lot of hot spots that look like nematode damage to me.

“What’s really bad is there’s not a whole lot producers can do about it. Picking up symptoms, identifying fields and getting a race analysis – which is what I’m begging producers to do – is about all that can be done. On the race: let’s figure out what we’ve got. It’ll cost a bit up front, but the investment can be recouped easily by being able to choose the proper, resistant variety and avoiding yield loss in the coming years.”

Typically, nematode damage shows up at the end of July and into August. But producers began picking up symptoms last week when temperatures hit 95 degrees for the first time this year.

“I feel like nematodes have been wearing roots out,” says Tingle. “But with mild temperatures and plentiful water, the symptoms weren’t visible. All that was needed was a trigger, and those hotter temperatures provided it. The rain and mild temperatures helped hide nematode symptoms.”

To have just a couple of hot days and immediately see nematode symptoms makes Tingle believe that the problem could be much more severe than what it now appears.

“These pests have already gotten organized and stressed the root systems out. All it took was a brief hot period – and not even a really stressful one considering most Arkansas summers – for this to surface. That’s scary – especially if the rains shut off. If it gets hot and dry now, we’re going to be in some real trouble.”

Once he plants a non-resistant soybean variety, any option a producer had to deal with nematodes is lost.

“And if you don’t know what race you’ve got, you’re shooting blind,” says Coker. “You must know what races are in your fields, period. Otherwise, you’re just gambling. Right now, it’s time to gather samples.

“The only thing that producers can do is to not stress their soybeans further. That’s especially true of water stress. So if an infested field can be irrigated, the producer should be very quick to crank up the pumps.”

Coker says if lower leafs on soybean plants are yellowing, producers should dig the plant up and check for nematodes.

Also, if the weather pattern the state is in continues, “producers should start looking for foliar diseases – aerial blight, frogeye leaf spot – at flowering. Another disease that we should be looking for is stem canker,” he says.

Tingle says in between field trips and speaking with agents around the state about nematodes, he’s working on a newsletter “that will help and educate agents and producers on identifying symptoms and sampling procedures. The newsletter should be out soon, so folks should be looking for it.”

Coker says the biggest problem producers face is lack of varieties resistant to nematode races now found in Arkansas. “I think we’ve backed ourselves into a corner by pushing for yield and ignored pests that can rob yield,” he says.

“If you look at the majority of the varieties we recommend, they’re resistant to Race 3 and Race 14,” says Tingle. “We’ve done surveys in a number of counties to find out what races we have and 3 and 14 aren’t the ones we have. We’ve got to work on our germ plasm because variety selection is our only defense against nematodes. This could easily become a statewide epidemic and we don’t have a single tool to combat it.

“I try not to push the panic button too quickly. But this is a legitimate concern and the sad thing is we can’t just go out and spray something to save these affected fields.”